Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field.
The various components of a device will often require some type of machining for optimum performance. The fine tolerances between the adjacent moving parts usually demand a high level of precision and accuracy during the machining processes. This is particularly true of tractor mounted, helical blade, lawn mowing assemblies and for convenience the present invention will be described with particular reference to this application. However, it will be appreciated that this is purely illustrative and in no way restrictive on the scope and application of the invention.
The grass on the fairways and greens of golf courses is often cut using a type of tractor mounted lawn mower. The mower has one or more elongate cylindrical reels formed by helically wound cutting blades. The reel assembly further includes a bedknife that has a blade that is parallel to the axis of the cylinder and positioned closely adjacent to its outer surface. The reel assembly is lowered so that the edge of the bedknife is at the required mowing height. As the reel is spun about its axis, the cutting edges of each helical blade move past the cutting edge of the bedknife at an angle. Blades of grass caught between the two are cleanly cut with a scissor action.
It is preferable to cut the grass using a clean scissor action rather than the tearing or shearing action from the blades of a flat disc style mower, because the resultant cut blade of grass has much less damage to its cellular structure. By minimising the cellular damage to the cut blades of grass, the risk of fungal infection is also minimised as there is less surface area exposed to spore germination, that is, amputation compared to crushing. Furthermore, less water is required to replace the moisture lost by transpiration from the bleeding tip of the blade and there is less “browning” or dead spots in the grass. This helps to provide a “true” playing or putting surface.
As the helical blades on the mower reel assemblies become worn, the gap between the cutting edge of the helical blade and the cutting edge of the bedknife starts to increase such that the grass tends to be cut less by a scissor action and more by a tearing or shearing action. The increased cellular damage associated with this brings with it the disadvantages discussed above. Therefore, there is a need to regularly sharpen and re-tune the cylindrical reel in relation to the bedknife.
One method commonly used by golf courses is known as “back lapping”. Using an abrasive lapping paste, the bedknife is tightened against the helical blades and then the reel is rotated so that the cutting edge of the knife and the blades are worn into each other. This requires the bedknife to be positioned firmly against the rotating blades which causes a braking effect on the reel. This increases engine wear, fuel consumption and deterioration of the cylinder bearings. With increased bearing wear comes an ever increasing rate of damage to the rotating blades.
Another commonly used method is to cylindrically grind the reel. This involves spinning the blades against a curved grinding surface that corresponds to the cylindrical surface of the reel. However, this still produces a large area of contact between the helical cutting blades and the cutting edge of the bedknife. Therefore, the excessive braking effect and its disadvantages still exist.
In light of this, it has been recognised that the helical blades require a cutting edge backed by a relief angle to cleanly cut the grass blades. When properly tuned to the bedknife, the cylinder can spin freely thereby minimising the wear and tear caused by the friction loads. To machine the required relief angle while tuning the helical blades to the bedknife requires high levels of precision. This demands large expensive grinding equipment of the type that is permanently mounted to the workshop floor. The substantial grinding equipment is necessary in order to keep any deflections in the freshly machined cutting edges within the required tolerances. Excessive deflections in the helical blades or the bedknife will result in contact that causes the braking effect or an unacceptable gap that tears rather than cuts. Only the wealthiest of golf clubs can afford to install such equipment and therefore it is common to find that the reel assemblies are transported to remote workshops for sharpening. This provides the required relief angle but has many time and cost disadvantages when compared to back lapping and cylindrical grinding.
It has been found that frequently the bedknife support, which mounts to bedknife to the reel, is not in parallel alignment with the bedknife. Consequently, the bedknife support may interfere with the scissor action between the helical blades and the bedknife, and thus also needs to be realigned and re-tuned in relation to the reel and the bedknife.